The use of counter-current distribution to examine the effect of damaging agents on DNA

Mammalian DNA's were separated using a counter-current distribution system for demonstrating alteration in secondary structure after heat denaturation and drug treatment. By using this method a complete separation of native and denatured DNA was achieved. Although the separation of DNA depends on the temperature used for denaturation, the counter-current distribution pattern did not follow exactly the hyperchromic shift. The results suggest that counter-current distribution offers a complementary approach for the study of DNA secondary structure as this method reveals alterations occurring over a wider temperature range than the increase in ultraviolet absorption. The changes in distribution pattern demonstrate cross-linkage occurring with nitrogen mustard and single-strand breaks following methylene dimethanesulphonate (MDMS) treatment in vitro.